EFFECT OF SILICA GEL PH ON CRYSTAL GROWTH. Perrin Hutcheson. Dylan Perese. The effect of silica gel pH levels on crystal growth has been experimentally determined by creating gels with 5 mL, 9 mL and 12 mL of acetic acid. The acidity was varied by the amount of acetic acid added to the silica gel samples which was 5mL, 9mL, and 12mL The average three acidities of silica gels were 7.6, 5.2, and 5.0 for the 5ml, 9mL, and 12mL samples respectively. Copper (II) Chloride crystals, lead crystals and lead iodide crystals were prepared in silica-gels of varying pH, each of which represented a redox reaction similar to that of the CuCl2 crystals: Fe(s) + Cu2+ è Fe2+(aq) + Cu(s). Laboratory work was carried out by applying principles of molar mass, solution chemistry, crystal growth, crystal nucleation, solubility, and laboratory skills such as measuring and massing out substances, using logger pro, using pH probes, and using electric stir machines. Crystals in gels containing 9 mL of acetic acid were observed to be more dense, larger, and longer than crystals in gels containing 5 mL and even12 mL of acetic acid. The effect of silica gel pH on crystal growth has been explained through the application of theories surrounding crystal growth and dissolution, diffusion, crystal environment, and the energy landscape. The surface energy theory explained how the level of pH leads to the inverse relationship between nucleation and crystal grow, while the diffusion reaction theory explained how the level of pH would affect the physical mechanism for crystal growth. Buffered gels were also created as control gels. The results mirrored the hypothesis for the most part, deviating only in that silica-gels prepared with 9 mL of acetic acid contained more developed crystals than those prepared with 12 mL of acetic acid. The significance of this lab lies in the fact that crystallization is relevant to real-world science, not just in solution or gel chemistry – and helps explain chemical bonding and even biological processes such as biomineralization. (which is how many animals produce minerals). Key words: solution-chemistry, assisted nucleation, surface energy theory molar mass, crystallization, pH, solubility, solute, solvent and silica-gels.
Figure 1: Results Graphic:
* = the crystal growth rating scale is an arbitrary method of representing observed trends for crystal growth. A rating of 0-5 indicates little or no crystal growth. Crystals assigned a rating of 0-5 will have increasing small, thin, less dense, or less-developed crystals, with a rating of 0 indicating no reaction. A rating of 5-10 indicates substantial crystal growth. Crystals assigned a rating of 5-10 are increasingly dense, developed, intricate, or long.
The data presented in this graph is intended to convey general trends observed in the lab. Note that a crystal growth rating of 3 for 5 mL of acetic acid represents both mildly developed crystals in the CuCl2 tube, and no crystal development in the lead and lead iodide tubes.
Figure 2: Crystals: Day 6:
Discussion of Lab, Journal Articles, & Results:
Works Cited: De Yoreo, JJ, & Vekilov, PG. (2003). Principles of Crystal Nucleation and Growth. In S. Weiner (Ed.),Biomineralization (pp. 57-93). Washington, D.C.: Mineralogical Society of America.
Newalkar, BL, Kamath, BV, Jasra, RV, & Bhat, SG. (1997). The effect of gel ph on the crystallization of aluminophosphate molecular sieve. Elsevier.
Figure 1: Results Graphic:
* = the crystal growth rating scale is an arbitrary method of representing observed trends for crystal growth. A rating of 0-5 indicates little or no crystal growth. Crystals assigned a rating of 0-5 will have increasing small, thin, less dense, or less-developed crystals, with a rating of 0 indicating no reaction. A rating of 5-10 indicates substantial crystal growth. Crystals assigned a rating of 5-10 are increasingly dense, developed, intricate, or long.
The data presented in this graph is intended to convey general trends observed in the lab. Note that a crystal growth rating of 3 for 5 mL of acetic acid represents both mildly developed crystals in the CuCl2 tube, and no crystal development in the lead and lead iodide tubes.
Figure 2: Crystals: Day 6:
Discussion of Lab, Journal Articles, & Results:
Works Cited:
De Yoreo, JJ, & Vekilov, PG. (2003). Principles of Crystal Nucleation and Growth. In S. Weiner (Ed.),Biomineralization (pp. 57-93). Washington, D.C.: Mineralogical Society of America.
Newalkar, BL, Kamath, BV, Jasra, RV, & Bhat, SG. (1997). The effect of gel ph on the crystallization of aluminophosphate molecular sieve. Elsevier.
Mulin, JW. (2001). Crystallization fourth edition. Woburn, MA: Butterworth-Heinemann.